Insect steroid metabolism is an attractive target for control of arthropod pests of agricultural and medical importance, since these organisms are unable to biosynthesize the steroid nucleus de novo. Chemicals which interfere with the degradation of phytosterols to cholesterol or the metabolism of cholesterol to molting hormones offer the opportunity of selectively preventing insect growth and development with minimal vertebrate toxicity. We propose a new class of steroidal compounds which selectively release a metabolic poison as the result of enzymatic activation by an insect or other arthropod. We propose to synthesize a variety of fluorinated phytosterols and to test them in vivo with several economically important anthropod pests, e.g., termites, cockroaches, and fire ants. Tests will also be performed with arthropod and mollusc vectors of infectious and parasitic human diseases, to extent the utility of these new latent phylum-specific pesticides. Mice will be employed to verify the hypothesized nontoxic nature of these compounds. Research quantities of successful candidate compounds will be made available to other workers to examine the species specifity and scope of these compounds as practical arthropod control agents.